The present invention relates to a structure for mounting a sensing element of a strain gauge type or the like which is provided in a vehicle such as a truck or the like to measure the load put on the vehicle.
Measurement of the load of the vehicle is made mainly for a large-sized vehicle such as a truck or the like not only in order to prevent the large-sized vehicle from causing a traffic accident such as a rollover or the like due to an overweight load, but also in order to prevent the promotion of deterioration of the vehicle and road surface.
Conventionally, the measurement of the vehicle load is made by putting the vehicle to be measured on a platform scale which is commonly referred to as "Kan-kan". However, such conventional measurement must be made in large-scale measuring facilities and requires a wide installation space. Thus, not only the number of platform scales that can be installed is limited, which makes it impossible to measure the loads of many vehicles, but also the installation cost of the platform scales increases.
In view of this, in recent years, there has been provided a load measuring device which is carried in the vehicle itself to measure the load.
In the conventional load measuring device of a vehicle onboard type, for example, in Japanese Patent Unexamined Publication No. Hei. 6-6814 which has been previously proposed by the present assignee, in the end portion of a shackle pin, there is formed a tapered hole which extends along the axial direction of the shackle pin, a sensing element including integrally therewith a tapered fixed member corresponding to the tapered hole of the shackle pin is press inserted into the tapered hole of the shackle pin and the fixed member is made to operate as a wedge, so that the sensing element can be fixed within the shackle pin.
By the way, before the fixing structure disclosed in the above-mentioned publication, there had been known a first fixing structure in which, in the end portion of a shackle pin, there is formed a hole, a through hole in communication with this hole is also formed in the shackle pin in such a manner that it starts from the outer periphery of the shackle pin and extends through the same, and, after a sensing element is stored into the shackle pin, adhesives are put into the interior portion of the hole from the through hole; and, there had also been known a second fixing structure in which, by applying a laser beam to the interior portion of a hole formed in a shackle pin, a sensing element is welded to the inner peripheral surface of the hole of the shackle pin. The sensing element fixing structure disclosed in the above publication is advantageous not only over the first fixing structure in that it is greater in the fixing strength than the first fixing structure, but also over the second fixing structure in that there is eliminated the need to carry out a troublesome operation requiring a high precision that the optical axis of the laser beam is finely matched to the through hole.
After then, in the above-mentioned fixing structure disclosed in the above-mentioned publication, not only in order to eliminate the possibility that, due to the degree of the force used when the sensing element is press inserted into the shackle pin, other forces than the actual load can be applied to the sensing element to make it impossible to obtain an exact output corresponding to the actual load, thereby being able to improve the precision of the load measurement, but also in order to avoid an increase in the manufacturing cost caused by the complicated shapes of the hole formed in the shackle pin and the fixed member portion of the sensing element, in Japanese Patent Application No. Hei. 7-124860, the present assignee has proposed the following improved sensing element mounting structure.
That is, in the improved proposal, there is employed a structure in which the sensing element is stored into and fixed to a case once, and the sensing element is then stored into the shackle pin together with the case. In particular, in such storage, the interior portion of the case is formed to the shape of the sensing element, the exterior portion of the case is formed to the shape of the hole of the shackle pin, and the case is press inserted into the shackle pin in a normal manner which does not use the above-mentioned wedge action, so that the case and sensing element can be fixed to the shackle pin.
According to the above-mentioned improved proposal, since the sensing element can be fixed to the shackle pin without using the wedge action, there is eliminated the trouble to pay attention to the degree of the force when the sensing element is press inserted into the shackle pin and, at the same time, the shapes of the hole of the shackle pin and the sensing element can be simplified to thereby be able to reduce the working costs thereof.
However, at any rate, in the fixing structure in which the case is press inserted into the shackle pin, a dimensional difference between the hole of the shackle pin and the outer shape of the case must be reduced in order to increase a friction force acting between the case and shackle pin. For this reason, not only tolerances between the inside diameter of the shackle pin and the outer shape of the case but also the roughness of the inner peripheral surface of the hole of the shackle pin and the outer peripheral surface of the case require precision, which makes it impossible to reduce the working costs thereof to a sufficient degree. That is, in the fixing structure, there is still left room to be improved.